There is existing footwear which consists of a foam heel or an air bag for absorbing shock. However, such design fails to utilize the energy from the foot and much energy is lost during the impact between the sole of the shoe and the ground.
U.S. Pat. No. 5,845,419 discloses footwear which includes a spring device. Such arrangement of the spring device causes discomfort to the user as the spring device limits the flexibility in bending the sole of the shoe. It is also difficult for the user to maintain proper balance with the springs engaged below the sole of the shoe only at the front and back position.
As the shoe sole will be bent by the user in action, the weight of the springs will make it uneasy for the user to bend the shoe sole. The user also has to apply extra force on the shoe sole to return it to the original flat position after bending. The user will find it quite uncomfortable in bending the shoe sole and returning it to the flat position when walking or running.
U.S. Pat. No. 6,751,981 discloses footwear which returns energy to the user. However, the spring device is engaged only on parts of the shoe, for example at the heel portion and the ball portion of the shoe. Much energy is lost during the impact of the other portions of the sole with the ground, for example at the toe area, which is not effectively transferred back to the user. This footwear fails to transmit energy continuously from the backward sole area to the forward sole area in a pace cycle. Much energy is lost and is not captured and rebound to the user.